This invention relates to fire resistant polycarbonate compositions and more particularly transparent, fire resistant polycarbonate compositions.
Plastics are increasingly being used to replace metals in a wide variety of applications, from car exteriors to aircraft interiors. Flame retardant plastics have been especially useful, particularly in applications such as housings for electronic devices. The use of plastic instead of metal decreases weight, improves sound dampening and makes assembly of the device easier. Flame resistance has been predominantly provided by halogenated flame retardants, especially bromine- and chlorine-based flame retardants. However, plastics employing halogenated flame retardants may release toxic gas when heated to elevated temperatures. As a result, bromine- and chlorine-free fire resistant materials are in demand for a wide range of applications.
Transparent, fire resistant polycarbonate products are widely used in various applications such as household appliances, computers, electronic devices and glazing material for the building and construction industry. Acceptable flame resistance in combination with transparency in a polycarbonate composition is presently achieved using halogenated polycarbonate building blocks together with one or more sulphonate salt based fire retardants such as potassium diphenylsulfon-3-sulphonate (KSS) or potassium-perfluorobutane-sulphonate (Rimar salt). The combination of the halogenated building blocks and the sulphonate salt based fire retardants results in a synergistic effect. While these materials do not burn, they could release toxic gas when heated to elevated temperatures.
Polysiloxanes are known to impart fire resistance to many plastics, including polycarbonate materials. The resulting materials are not likely to release toxic gas when exposed to high temperatures. Unfortunately, the commonly known polysiloxanes cause haziness in polycarbonate materials thus diminishing the desired transparency.
Accordingly there remains a need in the art for transparent, fire resistant polycarbonate compositions which are essentially free of halogens.
The above discussed and other drawbacks and deficiencies of the prior art are overcome or alleviated by a transparent, fire resistant polycarbonate composition comprising polycarbonate, poly(methylphenylsiloxane) and a salt based flame retardant, wherein the polycarbonate composition has a UL94 V0 rating for the fire resistance at thickness greater than or equal to about 1.6 millimeters.
The above discussed and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description.
The transparent, fire resistant polycarbonate composition comprises polycarbonate, poly(methylphenylsiloxane) and a salt based flame retardant wherein the polycarbonate composition has a UL94 V0 rating for the fire resistance at thickness greater than or equal to about 1.6 millimeters.
Unexpectedly, poly(methylphenylsiloxane), unlike most polysiloxanes, does not affect the optical properties of polycarbonate compositions. Thus, when poly(methylphenylsiloxane) is used in a polycarbonate composition in combination with a salt based flame retardant, such as KSS or Rimar salt, the resulting transparent polycarbonate composition is fire resistant. Transparent is herein defined as having a percent transmission of about 85 and a haze value of about 5 when measured according to ASTM D1003, which is incorporated herein by reference, at a thickness of 3.2 mm. Preferably the transparent polycarbonate composition has a percent transmission of about 90 and a haze value of about 2.
Such transparent polycarbonate compositions can obtain UL94 V0 ratings at 1.6 mm thickness, something previously achievable only with a bromine or chlorine based fire retardant.
In an important feature of the present composition, the polycarbonate is essentially free of halogens. Essentially free of halogen is herein defined as amounts insufficient to produce toxic fumes when burned. In general, therefore, the polycarbonate will comprise less than about 1.0, preferably less than about 0.5, and most preferably less than about 0.2 percent by weight of a halogen. As used herein, the terms xe2x80x9cpolycarbonatexe2x80x9d and xe2x80x9cpolycarbonate compositionxe2x80x9d includes compositions having structural units of the formula (I): 
in which at least about 60 percent of the total number of R1 groups are aromatic radicals and the balance thereof are aliphatic, alicyclic, or aromatic radicals. Preferably, R1 is an aromatic radical and, more preferably, a radical of the formula (II): 
wherein each of A1 and A2 is a monocyclic divalent aryl radical and Y1 is a bridging radical having one or two atoms which separate A1 from A2. In an exemplary embodiment, one atom separates A1 from A2. Illustrative non-limiting examples of radicals of this type are xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94S(O)xe2x80x94, xe2x80x94S(O2)xe2x80x94, xe2x80x94C(O)xe2x80x94, methylene, cyclohexyl-methylene, 2-[2.2.1]-bicycloheptylidene, ethylidene, isopropylidene, neopentylidene, cyclohexylidene, cyclopentadecylidene, cyclododecylidene, and adamantylidene. The bridging radical Y1 can be an unsaturated hydrocarbon group or a saturated hydrocarbon group such as methylene, cyclohexylidene or isopropylidene.
Polycarbonates may be prepared by reacting a dihydroxy compound with a carbonate precursor such as phosgene, a haloformate, a carbonate or a carbonate ester, generally in the presence of an acid acceptor and a molecular weight regulator. Useful polymerization methods include interfacial polymerization, melt polymerization, and redistribution. Dihydroxy compounds in which only one atom separates A1 and A2 are the most widely used. As used herein, the term xe2x80x9cdihydroxy compoundxe2x80x9d includes, for example, bisphenol compounds having general formula (III) as follows: 
wherein Ra and Rb each represent a monovalent hydrocarbon group and may be the same or different; p and q are each independently integers from 0 to 4; and Xa represents one of the groups of formula (IV): 
wherein Rc and Rd each independently represent a hydrogen atom or a monovalent linear or cyclic hydrocarbon group and Rxe2x80x2 is a divalent hydrocarbon group.
Some illustrative, non-limiting examples of suitable dihydroxy compounds include the dihydroxy-substituted aromatic hydrocarbons disclosed by name or formula (generic or specific) in U.S. Pat. No. 4,217,438, which is incorporated herein by reference. A nonexclusive list of specific examples of the types of bisphenol compounds that may be represented by formula (III) includes the following:
1,1-bis(4-hydroxyphenyl) methane;
1,1-bis(4-hydroxyphenyl) ethane;
2,2-bis(4-hydroxyphenyl) propane (hereinafter xe2x80x9cbisphenol Axe2x80x9d or xe2x80x9cBPAxe2x80x9d);
2,2-bis(4-hydroxyphenyl) butane;
2,2-bis(4-hydroxyphenyl) octane;
1,1-bis(4-hydroxyphenyl) propane;
1,1-bis(4-hydroxyphenyl) n-butane;
bis(4-hydroxyphenyl) phenylmethane;
2,2-bis(4-hydroxy-1-methylphenyl) propane;
1,1-bis(4-hydroxy-t-butylphenyl) propane;
bis(hydroxyaryl) alkanes such as 2,2-bis(4-hydroxy-phenyl) propane;
1,1-bis(4-hydroxyphenyl) cyclopentane; and
bis(hydroxyaryl) cycloalkanes such as 1,1-bis(4-hydroxyphenyl) cyclohexane.
It is also possible to employ two or more different dihydroxy compounds or copolymers of a dihydroxy compound with a glycol or with a hydroxy- or acid-terminated polyester or with a dibasic acid or hydroxy acid in the event a carbonate copolymer rather than a homopolymer is desired for use. Polyarylates and polyester-carbonate resins or their blends can also be employed. Branched polycarbonates are also useful, as well as blends of linear polycarbonate and a branched polycarbonate. The branched polycarbonates may be prepared by adding a branching agent during polymerization.
These branching agents are well known and may comprise polyfunctional organic compounds containing at least three functional groups which may be hydroxyl, carboxyl, carboxylic anhydride, and mixtures thereof. Specific examples include trimellitic acid, trimellitic anhydride, trimellitic trichloride, tris-p-hydroxy phenyl ethane, isatin-bis-phenol, tris-phenol TC (1,3,5-tris((p-hydroxyphenyl)isopropyl)benzene), tris-phenol PA (4(4(1,1-bis(p-hydroxyphenyl)-ethyl) alpha,alpha-dimethyl benzyl)phenol, trimesic acid and benzophenone tetracarboxylic acid. The branching agents may be added at a level of about 0.05-2.0 weight percent. Branching agents and procedures for making branched polycarbonates are described in U.S. Pat. Nos. 3,635,895 and 4,001,184 which are incorporated by reference. All types of polycarbonate end groups are contemplated as being within the scope of the present invention.
Preferred polycarbonates are based on bisphenol A, in which each of A1 and A2 is p-phenylene and Y1 is isopropylidene. Preferably, the average molecular weight of the polycarbonate is in the range of about 5,000 to about 100,000, more preferably in the range of about 10,000 to about 65,000, and most preferably in the range of about 15,000 to about 35,000. Furthermore the polycarbonate has a melt viscosity index (MVI) of about 4 to about 30 cm3/10 min.
Poly(methylphenylsiloxane) as used herein means a polymer having a plurality of units with the formula: 
Useful poly(methylphenylsiloxane)s have a viscosity of about 1 to about 300 centistoke (cSt) at 25xc2x0 C. Preferably the poly(methylphenylsiloxane) has a viscosity of about 4 to about 20 cSt and contains at least two silicon atoms in the polymer chain, and comprises internal methylphenylsiloxane units only. Additionally, copolymers of poly(methylphenylsiloxane) may be useful, wherein the polymer further comprises dimethoxysiloxane units. Preferably the number of methylphenylsiloxane units comprises greater than about 50%, more preferably greater than about 80%, and most preferably greater than about 90% of the total number of units.
Useful salt based flame retardants include alkali metal or alkaline earth metal salts of inorganic protonic acids as well as organic Brxc3x6nsted acids comprising at least one carbon atom. These salts should not contain chlorine and/or bromine. Preferably the salt based flame retardants are sulphonates and even more preferably they are selected from the group consisting of potassium diphenylsulfon-3-sulphonate (KSS), potassium-perfluorobutane-sulphonate (Rimar salt) and combinations comprising at least one of the foregoing. The poly(methylphenylsiloxane) and salt based flame retardant(s) are present in quantities effective to achieve a UL94-V2 and preferably a UL94 V0 flame resistant rating. Such quantities may be readily determined by one of ordinary skill in the art. In general, poly(methylphenylsiloxane) may be used in amounts of about 0.02 weight percent (wt %) to about 1.5 wt %, preferably 0.5 wt % to about 0.9 wt %, based on the total weight of the composition. Salt based flame retardants may be used in amounts of about 0.01 wt % to about 1.0 wt % based on the total weight of the composition. Preferably, when the salt based flame retardant is Rimar Salt, the amount of Rimar Salt is about 0.05 wt % to about 0.12 wt % based on the total weight of the composition. When the salt based flame retardant is KSS the amounts are 0.55 wt % or less, preferably 0.25 wt % or less based on the total weight of the composition.
The polycarbonate composition may include various additives ordinarily incorporated in resin compositions of this type. Such additives are, for example, fillers or reinforcing agents; heat stabilizers; antioxidants; light stabilizers; plasticizers; antistatic agents; mold releasing agents; additional resins; and blowing agents. Examples of fillers or reinforcing agents include glass fibers, glass beads, carbon fibers, silica, talc and calcium carbonate. Examples of heat stabilizers include triphenyl phosphite, tris-(2,6-dimethylphenyl)phosphite, tris-(2,4-di-t-butyl-phenyl) phosphite, tris-(mixed mono-and di-nonylphenyl)phosphite, dimethylbenzene phosphonate and trimethyl phosphate. Examples of antioxidants include octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, and pentaerythrityl-tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]. Examples of light stabilizers include 2-(2-hydroxy-5-methylphenyl)benzotriazole, 2-(2-hydroxy-5-tert-octylphenyl)-benzotriazole and 2-hydroxy-4-n-octoxy benzophenone. Examples of plasticizers include dioctyl-4,5-epoxy-hexahydrophthalate, tris-(octoxycarbonylethyl)isocyanurate, tristearin and epoxidized soybean oil. Examples of the antistatic agent include glycerol monostearate, sodium stearyl sulfonate, and sodium dodecylbenzenesulfonate. Examples of mold releasing agents include pentaerythritoltetrastearate stearyl stearate, beeswax, montan wax and paraffin wax. Examples of other resins include but are not limited to polypropylene, polystyrene, polymethyl methacrylate, and polyphenylene oxide. Combinations of any of the foregoing additives may be used. Such additives may be mixed at a suitable time during the mixing of the components for forming the composition.
The transparent, fire resistant polycarbonate composition may be made by intimately mixing the polycarbonate, poly(methylphenylsiloxane), and salt based flame retardant either in solution or in melt, using any known mixing method. Typically, there are two distinct mixing steps: a premixing step and a melt mixing step. In the premixing step, the ingredients are mixed together. This premixing step is typically performed using a tumbler mixer or a ribbon blender. However, if desired, the premix may be manufactured using a high shear mixer such as a Henschel mixer or similar high intensity device. The premixing step must be followed by a melt mixing step where the premix is melted and mixed again as a melt. Alternatively, it is possible to eliminate the premixing step, and simply add the raw materials directly into the feed section of a melt mixing device (such as an extruder) via separate feed systems. In the melt mixing step, the ingredients are typically melt kneaded in a single screw or twin screw extruder, and extruded as pellets.
The invention is further illustrated by the following non-limiting Examples.